Conventional motion picture film comprises frames that are commonly displayed sequentially at a frame rate of 24 frames per second (24 fps), 30 fps, or some other rate. Required special effects may be embodied in the displayed film.
Systems (including "telecone" systems) have been developed for converting motion picture film into video signals. These systems generate a video signal from motion picture film images by scanning the film frames sequentially to generate digitized film images. They then convert the digitized images into a video signal having a standard video frame rate (25 video frames per second for PAL video, 29.97 fps for NTSC video, or 30 fps for SMPTE-240M high definition video). Each video frame consists of two fields.
Conventional film scanning systems typically include circuitry for performing color correction on scanned images in real time (either before or after the images are digitized). To enable a user to perform color correction in a convenient manner, some conventional systems of this type are capable of generating a composite video signal comprising complementary portions of a color corrected image and a reference image, for split screen display on a video monitor.
During color correction, the user typically defines a "test" set of color correction parameters, and the system generates a "test" color corrected signal by processing one or more scanned film images in accordance with a color correction algorithm determined by the test set of parameters. The user then typically refines the test set of parameters to cause the system to produce a color corrected signal which, when displayed as a "test" image, has a color appearance matching that of a reference image.
In such a process, a split screen display usefully permits side-by-side comparison of a reference image with the latest test image.
However, until the present invention, split screen displays of this type had limited practical benefit. Often, the user could not readily distinguish between the two picture regions of the split screen display since the displayed reference and test images often differed only slightly and subtly in visual appearance.
In some prior art analog color correction systems, the user can define a window within a single digitized film image (for example, to select a set of color parameters that are defined by the image portion within the window). One such system is described in U.S. Pat. No. 4,694,329. In the system of U.S. Pat. No. 4,694,329, a window (of the type mentioned in this paragraph) can be surrounded by a border to distinguish the window from the remaining portion of the displayed single image. However, this type of conventional color correction system does not generate a composite signal from two or more digital signals representing two or more different images (for example, reference and scanned images) and does not generate a split-screen display having a border between picture areas in which different images are displayed. Thus, this type of conventional system does not enable the user conveniently to compare a reference image and a test image, and conveniently apply reference image color correction parameters to the test image by entering appropriate commands to the system.